PHYSICAL CHEMISTRY
PHASE DIAGRAM
Kontrak perkuliahan
• Penilaian :
UTS (40%) + UAS (40%) + tugas (20%)
• Persyaratan UTS/UAS : min kehadiran 80%
• Materi :
Diagram fasa :
 1 komponen
 2 komponen (solid – liquid, liquid – liquid,
liquid – vapor)
 3 komponen
Problems
•
•
•
•
•
•
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Apakah karbon dapat meleleh ?
Apakah karbon dapat menguap ?
Apakah helium dapat mencair ?
Apakah grafit dapat diubah menjadi intan ?
Apakah air dapat membeku pada suhu 60C ?
Apakah larutan garam selalu membeku pada suhu yg sama ?
Apa yg terjadi jika campuran metanol dan kloroform
dipanaskan ?
• Apa yg terjadi jika campuran logam tembaga dan nikel dalam
fasa cair didinginkan ?
Phase diagram
Aturan Fasa Gibbs :
F=C–P+2
F = derajat kebebasan
C = komponen
P = fasa
Phase diagram
• 1 komponen
• 2 komponen
• 3 komponen
 padat – cair
 cair – cair
 cair - uap
komponen = 3
fasa
=2
variabel = x1, x2, x3
F=C–P
komponen = 1
fasa
=3
variabel = p,T
F=C–P+2
komponen = 2
fasa
=2
variabel = p/T, x
F=C–P+1
Phase diagram
1 components
Clausius-Clapeyron equation
The solid-liquid curves
The liquid-vapor &
solid-vapor curves
The liquid-vapor and solid-vapor curves
For example, we can begin with the CO2 phase diagram.
The triple point for CO2 is 5.11 atm and 216.15 K.
The critical point for CO2 is 72.85 atm and 304.2 K.
The solid-liquid curves
P (atm)
……………
T (K)
…………….
Exercise
1. Sketch (roughly to scale) a phase diagram for
molecular oxygen given the following information: the
triple point occurs at 54.3 K and 1.14 torr; the critical
point occurs at 154.6 K and 37828 torr; the normal
melting point is 54.75 K; and the normal boiling point
is 90.25 K. Does solid molecular oxygen melt under
applied pressure?
2. Calculate the melting point of ice under a pressure of
50 bar given that the melting point at 1 bar is 0°C.
Assume that the density of ice under these conditions
is 0.92 g/mL and the density of liquid water is 1.00
g/mL. The molar enthalpy of fusion of water is 6.01
kJ/mol.
3. If it takes an increase of 1.334 megabars of pressure
to change the melting point of a substance from
222°C to 122°C for a change in molar volume of –3.22
cm3/mol, what is the molar enthalpy of fusion of the
substance in J/mol?
4. At what pressure does the boiling point of water
become 300°C? If oceanic pressure increases by 1
atm for every 10 m, to what ocean depth does this
pressure correspond?
Phase diagram
2 components
Solid - liquid
Examples of 2 immiscible
components (A & B) :
 CaAl2Si2O8 (calcic plagioclase) and FeMgSiO4
(olivine)
 olivine (isolated
tetrahedra) and pyroxene
(single chain tetrahedra)
They are immiscible because
they have different crystal
structures
Example :
melting ice & snow
in the winter
Example of ice
& snow melter
 NaCl
 MgCl2
 potassium acetate
Another example :
Describe the
process of 1 - 5
Phase diagram
2 components
Solid - liquid
Many binary systems
react to produce
different compounds
-one important
example is the
formation of GaAs
(gallium arsenide)
which is very
important for the
manufacture of III/V
semiconductors:
Chocolate-vanilla phase diagram
The chocolate-vanilla ice
cream phase diagram, as
shown in the accompanying
sketch, was developed at
the U.S. Navy’s famous
Steerage Research
Laboratories, located in
Annapolis. The men
responsible for this
development are Dr.
Christian of Cornell
University and Dr. Thor of
the University of Arizona
As can be seen, the most important area lies at the vanilla end of the diagram. The
chocolate end is of minor importance; the only commercially sound product is pure
chocolate. The eutectic is, of course, chocolate ripple. An interesting feature of the
diagram is the sloping solvus line. When a composition within the proper range is
allowed to thaw slightly, into the α region (a solid solution of chocolate in vanilla),
and is then cooled to a temperature below this line, flakes of chocolate precipitate
out, forming chocolate chips.
Phase diagram
2 components
Solid - liquid
Complete
miscibility in
both liquid and
crystal phases.
For example :
CaAl2Si2O8
(anorthite) and
NaAl2Si2O8
(albite)
Determining proportions of Phases
(the Lever Rule)
• The composition of each
phase is given by the each
end of the tie line
• The relative proportion of
each phase is given by the
length of the tie line
Example
• Rule : If we know T and Co, then we know:
--the composition of each phase.
At TA = 1320°C:
Cu-Ni
system
Only Liquid (L) present
CL = C0 ( = 35 wt% Ni)
At TD = 1190°C:
Only Solid (a) present
Ca = C0 ( = 35 wt% Ni)
At TB = 1250°C:
Both a and L present
CL = C liquidus( = 32 wt% Ni)
Ca = C solidus ( = 43 wt% Ni)
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Problems
1. A 53% Ni Cu-Ni alloy is cooled from liquid state to
1300 C. Calculate the % of liquid and solid at
1300 C. The tie line at 1300 C intersects solidus
at 58% Ni and liquidus at 45% Ni.
2. A 40% Pb-Sn alloy is cooled just below the eutectic
temperature. What is the fraction of proeutectic a
and  ? The eutectic point is at 61.9% Sn and a
boundary is at 19.2% Sn (see the phase diagram
below).
Drawing the phase diagram
• The mole fraction of A in the region near pure A varies with
temperature according to the equation below :
The melting points and heats of fusion of gold and silicon are
Au
Si
T0 (K)
1337
1683
Hfus (J/mol)
12.677,5
39.622,5
For the data calculate the solid-liquid equilibrium lines and
estimate the eutectic composition graphically !